1. Field of the Invention
The present invention relates to a semiconductor device of the tape carrier type and a display device including the same.
2. Description of the Related Art
Thin display devices typified by liquid crystal displays employ a semiconductor device for driving that inputs display signals. Such a semiconductor device is required to be thin and produce multiple output signals. Examples of the method of mounting such a semiconductor device include using a chip-on-glass (hereinafter, referred to as “COG”) structure or a tape-carrier-package (hereinafter, referred to as “TCP”) structure.
First, a semiconductor device mounted on a display device so as to have a COG structure will be described. FIG. 24 is a cross-sectional view of a semiconductor device mounted on a display device so as to have a COG structure. A display glass 109 as a transparent substrate is adhered onto a glass substrate 111 as a display substrate that is connected to a back light 110 as a light source. The region without the display glass 109 on the glass substrate 111 is a region for mounting a semiconductor chip 105, and transparent electrodes 112 are formed on this region. Electrodes 108 of the semiconductor chip 105 are connected to bumps 106 as protruding electrodes. The electrodes 108 and the transparent electrodes 112 are electrically connected to each other. Between the semiconductor chip 105 and the transparent electrodes 112, an anisotropic conductive film 113 containing conductive particles is provided, and the conductive particles contained in the anisotropic conductive film 113 serve to electrically connect the electrodes 108 and the transparent electrodes 112.
Next, a semiconductor device having a TCP structure will be described. Among semiconductor devices having a TCP structure, especially the one having a chip-on-film (hereinafter, referred to as “COF”) structure employs a film substrate that can be folded easily and thus can be handled easily.
Hereinafter, a semiconductor device having a COF structure will be described. FIG. 25 is a plan view of a conventional semiconductor device with a COF structure. FIG. 26 is a cross-sectional view taken in the arrow direction of line D-D′ in FIG. 25.
In the conventional semiconductor device, a semiconductor chip 105 is mounted on an insulating flexible film substrate 102 formed of a polyimide or the like, on which conductive leads 104 as wiring electrodes have been formed. Electrodes 108 of the semiconductor chip 105 are connected to the conductive leads 104 via bumps 106 as protruding electrodes. The bumps 106 may have various heights. Also, it is possible to produce the semiconductor device without using the bumps 106. The conductive leads 104 typically are plated.
The space between the semiconductor chip 105 and the film substrate 102 is filled with an encapsulation resin 107 so as to encapsulate the electrodes 108 of the semiconductor chip 105, thereby protecting the surface of the electrodes 108 and securing the strength of the semiconductor device itself. Outside the region where the encapsulation resin 107 is formed, a solder resist 103 is formed. The conductive leads 104 are exposed at a portion where the solder resist 103 is not formed.
Portions of the conductive leads 104 that contain the portions electrically connected to the electrodes 108 of the semiconductor chip 105 and are encapsulated in the encapsulation resin 107 are inner leads 104a. The inner leads 104a are in intimate contact with the film substrate 102. Because flying leads liable to bend are not present, it is possible to make the conductive leads 104 thin. Therefore, as compared with conventional TCP structures, the COF structure is advantageous in that the conductive leads 104 can be etched more easily, thereby making it possible to form finer conductor patterns.
On the other hand, portions of the conductive leads 104 exposed from the solder resist 103 are outer leads 104b and 104c, which are the portions to be connected to a display device when mounting the semiconductor device on the display device.
Hereinafter, a conventional way of mounting the semiconductor device having a COF structure will be described. FIG. 27 is a cross-sectional view of the semiconductor device with a COF structure mounted on a display device. In FIG. 27, a display device includes a back light 110, a glass substrate 111, and a display glass 109 laminated in this order. A PCB (printed circuit board) substrate 114 for supplying power and signals to the semiconductor device is mounted on the back light 110 side of the glass substrate 111. The conductive leads 104c on one end of the semiconductor device having a COF structure are connected to electrodes 115 of the PCB substrate 114 via the anisotropic conductive film 113. The film substrate 102 is bent toward the semiconductor chip 105 side, and the outer leads 104b on the other end of the semiconductor device are connected to the transparent electrodes 112 formed on the display glass 109 side of the glass substrate 111 via the anisotropic conductive film 113.
In the display device having the above-described configuration, power and signals supplied from the PCB substrate 114 are input to the semiconductor chip 105 from the outer leads 104c. After being processed by the semiconductor chip 105, the power and signals are transmitted from the outer leads 104b to the glass substrate 111 via the transparent electrodes 112.
In the conventional semiconductor device having a COF structure, the film substrate 102 is formed so as to extend from one surface to the other surface of the glass substrate 111. Thus, the film substrate 112 is required to have a long length, which brings about the problem in that the cost of the semiconductor device is increased due to the high cost of the film substrate. Another problem is that, because a plurality of the same driving ICs are mounted, the PCB substrate 114 for supplying them with power and signals for operating a semiconductor chip needs to be provided, which increases the cost of the display device.
In the case of the semiconductor device mounted on a display device so as to have a COG structure as described above, no cost is required for a film because no film is used therein. However, because rigid substrates such as the semiconductor chip 105 and the glass substrate 111 are joined to each other via the bumps 106, variations in height of the bumps 106 are liable to occur and cause unstable contact at the joined portion, which may result in bad electrical contact between the semiconductor chip 105 and the glass substrate 111. In addition, because the semiconductor device is mounted on the glass substrate 111 directly with only an ACF (anisotropic conductive film) or the like intervening therebetween, the display device is susceptible to the influence of the heat generated by the semiconductor chip 105 and mechanical stress caused by the difference in thermal expansion coefficient among the semiconductor chip 105, the glass substrate 111, and the anisotropic conductive film 113. This may bring about the problem in that the deterioration of the quality of display, such as irregularity in display or the like, occurs in the vicinity of the portion for mounting the semiconductor device.
Other examples of a semiconductor device having a COF structure are disclosed in JP 6(1994)-349898 A, JP 11(1999)-354589 A, JP 2000-195898 A, JP 2001-237280 A, etc.